臺灣南部藍綠光鰓雀鯛(Chromis viridis)生殖習性研究

Abstract

本研究以墾丁核能三廠入水口的藍綠光鰓雀鯛(Chromis viridis, Cuvier 1830)做為研究材料，研究其生殖習性。在本區海域中，藍綠光鰓雀鯛終年都會生殖。於2011年1月至2012年11月，每月進行實地潛水觀察其生殖現象，並於2011年11月至2012年7月間共進行7次定點錄影。為了檢視領域性雄魚在整個生殖進程中，從築巢、求偶產卵到護卵，其行為組成上的變化，以2012年4月11至13日及2012年7月10日至12日定點錄製的影像作分析。首先將個體的行為區分成以下幾種：skimming(SK)、hovering(H)、signal jumping(SJ)、circling(C)、aggression(A)、leaving(L)、nipping(N)、interfering(I)、fleeing(F)等9種，並依其發生順序及經過時間，加以記錄。 於築巢期(4月12日；7月10日)，領域性雄魚一邊在清理海底基質、準備生殖巢，一邊在為之後的求偶進行準備，此時其行為的發生具有明確的序列(SK → H → N)。到了之後的求偶產卵期（4月13日；7月11日），求偶產卵的行為以(SJ → C)為主要組成，同時，(C →I)的發生率亦髙，亦即產卵行為常會受其它領域性雄魚或水層中的雌魚干擾而中斷。在護卵期（4月份無資料；7月12日），雄魚大多數時間離巢至水層覓食(佔總觀察時間的90.92%)，小部份時間則會留在巢內護卵(SK + H：9.08%)。一般經過約3天，仔魚即孵化，而後護卵的雄魚會離開產卵場，回到其攝食魚群。在雄魚築巢的過程中，雌魚多在水層中覓食，到了雄魚的求偶期，雌魚會聚集在生殖區域上方水層，接受雄魚的引導，到後者的巢中產卵。 藍綠光鰓雀鯛的生殖活動，除了經由領域性雄魚求偶來完成的典型形式，另發生有群集生殖(group spawning)的現象。群集生殖出現在求偶產卵期：在產卵高峰時期，有一些未擁有領域的雄魚會混雜在雌魚魚群，一起進入產卵場內，進行生殖。此雌、雄混雜的群體，從水層中快速集結，不經領域性雄魚求偶，自行進入數隻雄魚相鄰的領域，在其基質上產卵，之後迅速離開。群集生殖多會重複發生在同一基質上。群集生殖群中的雄性個體，體型明顯小於領域性雄魚(p<0.05)；而群集生殖群中雌魚與雄魚兩者在體長間並無顯著差異(p>0.05)。 群集生殖群離開之後，原領域性雄魚留在巢內，繼續進行生殖活動。比較有、無遭受群集生殖群入侵之間的行為組成得知，被侵入者離開巢位的時間明顯增加；同時，求偶頻率與成功率降低。未受入侵的雄魚求偶頻率為29.17%，而受入侵的雄魚則僅剩12.73%；未受入侵雄魚有42%的機會從SJ進入C，遭入侵的領域的雄魚僅有37%，顯示群集生殖會影響到其所入侵的領域性雄魚的求偶及交配強度。對遭入侵的領域性雄魚而言，群集進來的雌魚已在其巢中以及相鄰的基質上所產的卵，部分可能已經為混在其中的雄魚所受精，但是領域性雄魚也可能從中獲得受精的機會，故我們推測這是這些領域性雄魚會留在原處，繼續顧巢、護卵的原因。 研究區域內藍綠光鰓雀鯛群集生殖現象的發生，可能是由兩個因素所造成：（一）成熟雌魚過多，有很多沒有機會被求偶的個體，靠著成群強勢進入合適的巢區，逕自進行產卵。（二）由於環境中產卵基質不足，使得一些沒有辦法取得基質的雄魚個體，混在雌魚群中趁機進行受精，而達到生殖的目的。

Reproductive characteristics of the blue-green damselfish (Chromis viridis, Cuvier 1830) in the water inlet of the 3rd Nuclear Power Plant at Kenting were studied. The fish spawns year-round in the study area. Observations of its reproductive behaviors were conducted using SCUBA monthly from January 2011 to July 2012, and between November 2011 and July 2012 we conducted underwater video recordings in a total of 7 days at specific spawning sites. To examine changes in actions of the territorial males in various spawning phases, i.e., nest-preparation, courtship and egg-caring, we analyzed the content of video recordings taken on April 7~13 and July 10~12, 2012. Firstly, actions of the territorial male were divided into 9 patterns: skimming(SK), hovering(H), signal jumping(SJ), circling(C), aggression(A), leaving(L), nipping(N), interfering(I) and fleeing(F). Then the occurring sequences of these actions were recorded. During nest preparation, territorial males cleaned up the substratum, making the nest ready for the forthcoming courtship. In this phase, their actions followed specific trends (i.e., SK → H → N). During courtship and spawning phase, the sequence of (SJ → C) prevailed. However, the sequence of (C → I) was also noticeable, indicating that spawning could be frequently interrupted by the interference of other males and or females. During eggs-caring phase, territorial males spent most of their time feeding in water column (for 90.02% of the actions taken). The remaining 9.08% was attributed to the egg-caring motion (i.e., SK + H). After a 3-day spawning session, eggs hatched; the territorial male left the nest and back to the feeding school. When the male was preparing the nest, the female would stay and feed in the water column nearby. When courtship began, females would aggregate above the spawning area and the female who accepted the male’s courtship would follow the male back to and spawn on his nest. In addition to the above spawning pattern, in which the spawning was led by the courtship of the territorial male, an alternative spawning pattern, so called ‘group spawning’, also occurred in the blue-green damselfish. Group spawning had happen in the high peak of courtship period. In this moment, without any sign of courtship invitation from the nesting male, some un-territorial males would join the females in approaching the territorial males’ nest, where they together rushed and subsequently spawned on the substratum normally defended by the nesting males. After a swift spawning session, most for less than one minute, the intruding group would leave and return to their previous school. Group spawning had occurred repeatedly on the same substratum. The male in the group was significantly smaller than the nesting males in the body size (fork length). By contrast, in the same intruding group there was no body-size difference between the male and the female. After the intrusion, the territorial male would stay in the nest and proceed its spawning. Comparisons of the behaviors between territorial males with or without the intrusion of group spawners showed that the fish experienced intrusion had spent less time in the nest. Meanwhile both their courting activity (12.73% vs. 29.17%) and their success rate in courtship (37% vs.53%) had declined. Why did the intruded males stay and keep defending their nests? In the group spawning, the male could only fertilize a part of the eggs spawned by the companying female. This has left with an opportunity for the nest owner to fertilize and adopt the remaining eggs. This might answer the question asked. Group spawning is unusual in the damselfish spawning. For the blue-green damselfish, in the study area there were so many mature females; for those who do not have the opportunity of being courted, have to adopt an alternative strategy to insure individual’s fitness. Invading to suitable nests and spawning on them could be one that was adopted by the female. On the other hand, due to the limitation of suitable nesting substrate, those males who could not take its possession of nesting substrate might just join the female, sneak to the nests, and fertilize eggs.